<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo3</title>

</head>
<body>
<script src="vue.global.js"></script>
<div id="app">
<button @click="num--">-</button>
<span>{{ num }}</span>
<button @click="num++">+</button>
</div>
<script>
    const app = Vue.createApp({
        data(){
            return{
                num:20
            }
        }
    }).mount('#app')
</script>
</body>
</html>
